Update maven Docker tag to v3.8.1

This MR contains the following updates:

Package	Type	Update	Change
maven	ironbank-docker	minor	3.6.3-openjdk-8 -> 3.8.1-openjdk-8
maven		minor	3.6.3 -> 3.8.1
maven	stage	minor	3.6.3-openjdk-8 -> 3.8.1-openjdk-8

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